The recent identification of transcription factors (TFs) that can induce conversion of fibroblasts into pluripotent stem (iPS) cells makes it potentially possible to generate patient-specific neurons from fibroblasts. However, the neurons thus produced are difficult to obtain. The present project builds on preliminary results in which we demonstrate direct conversion of adult fibroblasts cells into neurons, referred to as 'induced neuronal cells' (iN cells), without an iPS intermediate. The resulting iN cells have the functional properties of neurons, including the ability to form functional synapses as assayed by electrophysiology. Thus, the iN cell technology provides a novel, more facile approach to generating and studying human neurons, and opens up a new avenue to investigating human disease processes. However, at this point the iN cell technology has only been developed for mouse fibroblasts, fundamental questions regarding the conversion process and the molecular identity of iN cells were not determined, the generation of iN cells from human fibroblasts has not yet been established, and most importantly, the feasibility of the iN cell technology to study diseases affecting neuronal function has not been demonstrated. In this project, we propose to address these important challenges in an interdisciplinary approach capitalizing from the combined expertises of the Wernig and Sidhof laboratories. We propose experiments that will systematically investigate the cellular and molecular identity of iN cells, and develop protocols to induce specific neuronal subpopulations from fibroblasts. These protocols will then be employed to model genetic diseases in mouse iN cells. Furthermore, we will extend our findings to human fibroblasts, with the long term goal to establish a cell model for neuropsychiatric diseases. Our goals will be pursued by a combination of tissue culture experiments with cells cultured from mice and humans, cell biology, molecular biology, and electrophysiology. We believe our proposed experiments have the potential to fundamentally change existing paradigms of cellular differentiation and epigenetic gene regulation, and could provide a novel platform to study human neurons from patients suffering from a variety of brain diseases.